class_docstr: Represents an autoregressive integrated moving-average (ARIMA) model.
  
  An [autoregressive moving-average (ARMA)](
  https://en.wikipedia.org/wiki/Autoregressive_moving_average_model) process is
  defined by the recursion
  
  ```
  level[t + 1] = (
      level_drift
      + noise[t + 1]
      + sum(ar_coefficients * levels[t : t - order : -1])
      + sum(ma_coefficients * noise[t : t - order : -1]))
    noise[t + 1] ~ Normal(0., scale=level_scale)
    ```
  
  where `noise` is an iid noise process. An integrated ([ARIMA](
  https://en.wikipedia.org/wiki/Autoregressive_integrated_moving_average))
  process corresponds to an ARMA model of the
  `integration_degree`th-order differences of a sequence, or equivalently,
  taking `integration_degree` cumulative sums of an underlying ARMA process.
code: def initial_state_prior(self):
      return self._initial_state_prior
  
imports: import tensorflow.compat.v2
  from tensorflow_probability.python.bijectors import chain
  from tensorflow_probability.python.bijectors import identity
  from tensorflow_probability.python.bijectors import scale
  from tensorflow_probability.python.bijectors import softplus
  from tensorflow_probability.python.bijectors import tanh
  from tensorflow_probability.python.distributions import linear_gaussian_ssm
  from tensorflow_probability.python.distributions import lognormal
  from tensorflow_probability.python.distributions import mvn_diag
  from tensorflow_probability.python.internal import dtype_util
  from tensorflow_probability.python.internal import prefer_static
  from tensorflow_probability.python.sts.components.autoregressive_moving_average import AutoregressiveMovingAverageStateSpaceModel
  from tensorflow_probability.python.sts.internal import missing_values_util
  from tensorflow_probability.python.sts.internal import util
  from tensorflow_probability.python.sts.structural_time_series import Parameter
  from tensorflow_probability.python.sts.structural_time_series import StructuralTimeSeries
label_desc: Use image node_id 2 for calling the AutoregressiveIntegratedMovingAverage obj's underlying member method code with example usage: obj.initial_state_prior() and returns: self